Most of us have the tendency to think in 3 dimensions when it comes to UFO sightings. Questions about distance, speed, and energy required to go from their planet to ours are usually what people bring up. But what if the UFOs were beings who were on a completely different dimension beyond what we're capable of perceiving. Check out this explaination of dimensions beyond lenth/width/depth/time:
https://youtube.com/watch?v=qU1fixMAObI